Spatial distribution of minority-carrier lifetime and local concentration of impurities in multicrystalline silicon solar cells

Spatial distribution of minority-carrier lifetime (τ) in multicrystalline silicon solar cells was investigated. By mapping of τ, a wide distribution in a higher-efficiency cell and a narrow distribution in a lower-efficiency cell was found, respectively. Based on the relation between τ and the density of grain boundaries, spatial distribution of impurities was characterized by secondary ion mass spectrometry. To clarify the spatial profile near grain boundaries, a method of changing detection area was carried out. Iron (Fe) segregation within 100 μm around a grain boundary was observed. In the lower-efficiency cell, a measurable amount of Fe was contained in a crystalline area as well.